Skin calcium-binding protein: effect of vitamin D deficiency and vitamin D treatment

The amount of skin calcium-binding protein, evaluated using a sensitive radioimmunoassay and indirect immunofluorescence, was decreased in vitamin-D deficient rats and increased after one week vitamin D3 or 1 alpha-hydroxyvitamin D3 treatment. In vitamin D replete and in vitamin D-deficient animals, skin calcium-binding protein was not sensitive to changes in dietary and/or serum calcium concentrations. These results indicate that this protein is different from other calcium-binding proteins such as parvalbumin and calmodulin which are not vitamin D-dependent, and also different from intestinal calcium-binding protein which, in D replete animals, is sensitive to changes in dietary and serum calcium concentrations. Skin calcium-binding protein may, therefore, represent a new class of vitamin D-dependent protein.     

A human skin equivalent model that mimics the photoproduction of vitamin D3 in human skin

Summary A human skin equivalent was prepared by culturing human keratinocytes on the surface of nylon filtration meshes containing human skin fibroblasts and by growing the epidermal cells at the air-liquid interface. This human skin equivalent model was used to mimic the photoproduction of vitamin D₃ in human skin. It was found that the concentration of 7-dehydrocholesterol and its photoconversion to previtamin D₃ and its subsequent thermal isomerization to vitamin D₃ in the human skin equivalent was essentially identical to that of human skin. The 7-dehydrocholesterol content in the skin equivalent and human skin was 2187±296 and 2352±320 ng/cm², respectively. The percentage of the major photoproducts of 7-dehydrocholesterol in the skin equivalent following ultraviolet B radiation (0.5 J/cm²) was 35% previtamin D₃, 29% lumisterol, and 6% tachysterol; 30% remained as 7-dehydrocholesterol. Similarly, in human skin they were 36%, 29%, 7%, and 28%, respectively. After incubation at 37°C for 30 min, 11% and 12% of the previtamin D₃ had thermally isomerized to vitamin D₃ in the skin equivalent and human skin. In conclusion, compared with cultured keratinocytes or fibroblasts, the human skin equivalent model provides a superior in vitro system that better mimics the physiology and biochemistry of the photosynthesis of vitamin D₃ in human skin.     

The rapid effects of 1,25-dihydroxyvitamin D3 require the vitamin D receptor and influence 24-hydroxylase activity: studies in human skin fibroblasts bearing vitamin D receptor mutations

If both rapid and genomic pathways may co-exist in the same cell, the involvement of the nuclear vitamin D receptor (VDR) in the rapid effects of 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) remains unclear. We therefore studied rapid and long term effects of 1,25-(OH)(2)D(3) in cultured skin fibroblasts from three patients with severe vitamin D-resistant rickets and one age-matched control. Patients bear homozygous missense VDR mutations that abolished either VDR binding to DNA (patient 1, mutation K45E) or its stable ligand binding (patients 2 and 3, mutation W286R). In patient 1 cells, 1,25-(OH)(2)D(3) (1 pm-10 nm) had no effect on either intracellular calcium or 24-hydroxylase (enzyme activity and mRNA expression). In contrast, cells bearing the W286R mutation had calcium responses to 1,25-(OH)(2)D(3) (profile and magnitude) and 24-hydroxylase responses to low (1 pm-100 pm) 1,25-(OH)(2)D(3) concentrations (activity, CYP24, and ferredoxin mRNAs) similar to those of controls. The blocker of Ca(2+) channels, verapamil, impeded both rapid (calcium) and long term (24-hydroxylase activity, CYP24, and ferredoxin mRNAs) responses in patient and control fibroblasts. The MEK 1/2 kinase inhibitor PD98059 also blocked the CYP24 mRNA response. Taken together, these results suggest that 1,25-(OH)(2)D(3) rapid effects require the presence of VDR and control, in part, the first step of 1,25-(OH)(2)D(3) catabolism via increased mRNA expression of the CYP24 and ferredoxin genes in the 24-hydroxylase complex.     

Glyoxylate cycle in the rat liver: effect of vitamin D3 treatment

Evidence for the glyoxylate cycle in the mammalian rat liver was sought. Activity of two unique glyoxylate cycle enzymes, isocitrate lyase and malate synthase, was found in rat liver homogenates. Vitamin D3 treatment of rachitic animals produced a five- and fourfold increase, respectively, in the activity of these enzymes. Vitamin D3 also increased the peroxisomal fatty acid oxidation and the accumulation of glycogen in liver slices in the presence of palmitate. These data suggest that the mammalian rat liver can convert fatty acid carbon to carbohydrate carbon directly.     

Shift work and depressive symptoms: the mediating effect of vitamin D and sleep quality

Shift work is associated with vitamin D level, sleep quality, and depressive symptoms. Vitamin D and sleep quality are also associated with depressive symptoms. The purpose of this study was to compare vitamin D level, sleep quality, and depressive symptoms between shift workers and daytime workers and analyze the mediating effect of vitamin D and sleep quality between shift work and depressive symptoms. Among those who participated in the Kangbuk Samsung Health Study in 2012 and 2014, 82,078 cases of full-time workers were analyzed. We evaluated their shift work, vitamin D level, sleep quality, and depressive symptoms with blood samples and questionnaires. Chi-square tests, t-tests, and path statistical analysis were performed. More depressive symptoms, lower vitamin D levels, and poorer sleep quality were associated with shift work. According to a path analysis, shift work had both a direct effect and an indirect effect on depressive symptoms, each mediated by sleep quality and vitamin D level. When a multigroup analysis was conducted for each sex, paths containing sleep quality were more significant in female shift workers than male shift workers; paths involving vitamin D did not differ between sexes. To assess depression risk in shift workers, evaluating vitamin D level and sleep quality is essential. Also, sleep problems are more prevalent in female compared to male shift workers with respect depression prevalence.     

Manipulation of environmental variables and the effect on the growth of Haliclona sp.: Implications for open-water aquaculture

We examined how the physical environment influences the growth and survival of an undescribed Haliclona species. To determine the influence that water movement, light and sediment had on the sponge, explants of Haliclona sp. (approximately 8 cm³ in size) were transplanted into manipulated microenvironments at Hamelin Bay on the west coast of Western Australia near Perth. The sponge is typically found under limestone ledges and appears to have distinct limits on the microenvironment in which it is found. A three-factor orthogonal design was used to manipulate levels of light, water flow and sedimentation. Each factor had two experimental levels, creating environments with high and low water movement, high and low light, and upward and downward orientations to control sediment levels. The survival of explants was high (100%). However, all explants showed a regression in weight. Explants transplanted on to the underside of horizontal surfaces (downward orientations) demonstrated significantly less weight loss (P = 0.023), which was attributed to lower sediment exposure. Light and water movement did not significantly influence the sponge's growth.     

Up-regulation of the intestinal 1,25-dihydroxyvitamin D receptor during hypervitaminosis D: a comparison between vitamin D2 and vitamin D3

Concentrations of intestinal 1,25-dihydroxyvitamin D receptor were measured in rats receiving pharmacological amounts (25,000 IU/rat daily for 6 days) of either vitamin D2 or vitamin D3. The data showed that both hypervitaminosis D2 and hypervitaminosis D3 resulted in significant up-regulation of intestinal 1,25-dihydroxyvitamin D receptor (fmol/mg protein) relative to controls (409 +/- 24, vitamin D2-treated; 525 +/- 41, vitamin D3-treated; and 249 +/- 19, control). The 1,25-dihydroxyvitamin D receptor enhancement also was accompanied by elevated plasma 25-hydroxyvitamin D and hypercalcemia. These data suggest that increased target-tissue 1,25-dihydroxyvitamin D receptor may play a role in enhancing target-tissue responsiveness and, thus, have a significant role in mediating the toxic effects of hypervitaminosis D.     

Side-chain oxidation of vitamin D3 in mouse kidney mitochondria: effect of the Hyp mutation and 1,25-dihydroxyvitamin D3 treatment

Side-chain oxidation of vitamin D is an important degradative pathway. In the present study we compared the enzymes involved in side-chain oxidation in normal and Hyp mouse kidney. Homogenates of normal mouse kidney catalyze the conversion of 25-hydroxyvitamin D3 to 24,25-dihydroxyvitamin D3, 24-oxo-25-hydroxyvitamin D3 and 24-oxo-23,25-dihydroxyvitamin D3. After subcellular fractionation, total side-chain oxidative activity, estimated by the sum of the three products synthesized per milligram protein under initial rate conditions, coincided with the mitochondrial enzyme marker succinate-cytochrome-c reductase. Treatment of normal mice with 1,25-dihydroxyvitamin D3 (1.5 ng/g) resulted in an eightfold increase in mitochondrial enzyme activity, with no change in apparent Km but a significant rise in Vmax. With 24,25-dihydroxyvitamin D3 as the substrate, normal renal mitochondria produced 24-oxo-25-hydroxyvitamin D3 and 24-oxo-23,25-dihydroxyvitamin D3, and the synthesis of these metabolites could be increased sixfold by pretreatment with 1,25-dihydroxyvitamin D3. In the Hyp mouse, the side-chain oxidation pathway showed similar subcellular distribution of enzyme activity. However, product formation from 25-hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 was twofold greater in mutant than in normal mitochondria. Furthermore, 1,25-dihydroxyvitamin D3 pretreatment of Hyp mice resulted in a 3.4-fold increase over basal metabolism of both 25-hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3. These results demonstrate that (i) kidneys from normal and Hyp mice possess basal and 1,25-dihydroxyvitamin D3 inducible enzyme system(s) in the mitochondrial fraction, which catalyze the side-chain oxidation of 25-hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3, and (ii) the Hyp mutation appears to perturb the renal metabolism of both substrates only in the basal state.     

The effect of environmental variables on the structure and function of hemocyanin fromCallianassa californiensis

Summary Callianassa, an estuarine animal, can experience changes in salinity which reduce the level of divalent cations in the blood, as well as changes in temperature and variations in protein concentration in the hemolymph. The hemocyanin in whole hemolymph shows evidence of dissociation ( 12%) after 3 days acclimation to 40% seawater. Using purified hemocyanin the dissociation from 39 S to 17 S hemocyanin was investigated for the three variables, salinity, temperature and protein concentration. An equation was developed to define the amount of dissociation which should be observed under physiological conditions.